A thermosetting fluororesin coating material is excellent in weather resistance, and because of this feature, it is widely used for bridges, gates, fences, building materials such as siding materials for houses, automobile bodies, and household electric appliances. As a coating film applied by coating, from an aesthetical viewpoint, there may be a case where gloss is required or a case where matting is required. Particularly, in recent years, a demand for a matte coating material has increased as it presents a high-grade appearance.
On the other hand, a powder coating material has a feature that it is solvent free, and its application range has been expanded in recent years, as consciousness for environmental protection has increased. Especially, a fluororesin powder coating material is capable of meeting a demand for maintenance free by virtue of the weather resistance performance which the fluororesin specifically has, and its applications are expected to increase.
With such a powder coating material, it has heretofore been common to employ a method wherein pigment particles of e.g. white carbon are added to present fine irregularities on the surface, or a method wherein wax or the like which is likely to bleed out on the surface, is added to provide a thin layer made of wax or the like on the coating film surface.
Further, JP-A-64-1770 proposes a resin composition for powder coating material comprising a polyester having a hydroxyl value of at least 1200 geq/106, a polyester having a hydroxyl value of from 200 to 1000 geq/106 and a blocked isocyanate curing agent, wherein the difference in gelation time between the two polyesters is at least 3 minutes. Further, JP-A-4-214771 proposes a resin composition for powder coating material comprising a polyester A having an acid value of at least 1200 geq/106, which is not substantially gelled, a polyester B having an acid value of from 200 to 1000 geq/106, which is not substantially gelled, and a triglycidyl isocyanate curing agent, wherein the difference in gelation time between the two polyesters is at least 3 minutes.
However, in the method of adding white carbon, pigment particles are present substantially on the coating film surface, and in the method of adding wax, the coating film surface is not a fluororesin, whereby there has been a problem that as compared with a coating film made of a fluororesin itself, the weather resistance performance is inferior. Further, so long as the above-mentioned methods are employed, the 60° specular gloss value can not be lowered to a level of 40%, and it has been very difficult to obtain a smooth coating film surface having a gloss of not higher than 40% which is desired in many cases.
In the resin composition disclosed in JP-A-64-1770 and in the resin composition disclosed in JP-A-4-214771, in order to obtain a matte effect, the acid value or the hydroxyl value of one of the polyester resins is made considerably high. Nevertheless, as they are made of polyesters, they are obliged to be poor in weather resistance. Further, when the two resins have the same type of functional groups, the matte effect tends to be inadequate.